Some biochemical activities of 10,10-Difluoro-13-dehydroprostacyclin, a chemically stable analog of prostacyclin, in human blood platelets

10,10-Difluoro-13-dehydroprostacyclin (DF 2-PGI 2) is a chemically stable analog of prostacyclin (PGI 2). DF 2-PGI 2 was 6 times more potent than prostaglandin E 1 (PGE 1), and 1/10 as potent as PGI 2 as an inhibitor of arachidonic acid (AA)-induced platelet aggregation. DF 2-PGI 2 also inhibited platelet aggregation induced by collagen, ADP, epinephrine and two thromboxane agonists, 9,11-azoPGH 2 and SQ 24,810 (9,11-epoxy-9α-homo-5(Z), 13(E)-15β-hydroxyprostadienoic acid, racemic mixture). The antiaggregatory effects by DF 2-PGI 2 and PGI 2 on AA-induced platelet aggregation were potentiated by etazolate (SQ 20,009), a potent inhibitor of cyclic AMP phosphodiesterase (PDE), and were blocked by SQ 22,536 (9-(tetrahydro-2-furyl) adenine), an inhibitor of adenylate cyclase (AC). DF 2-PGI 2 was also more potent than PGE 1, and less potent than PGI 2 as a stimulator of AC activity in platelet homogenates. DF 2-PGI 2- and PGI 2-stimulated AC activity was inhibited by a series of AC inhibitors, SQ 22,536, SQ 4,647 (9-furfuryl adenine) and 2′,5′-dideoxyadenosine. Furthermore, SQ 22,536 inhibited DF 2-PGI 2- and PGI 2-stimulated AC activity in a concentration-related manner, with 150 values of 150 and 300 μM, respectively. Finally, PGE 1, DF 2-PGI 2 and PGI 2, at 0.35 μM induced 2-, 10- and 17-fold increases, respectively, in cyclic AMP levels of intact platelets in platelet rich plasma (PRP). The increase in cyclic AMP levels by PGI 2 and DF 2-PGI 2 in PRP was also blocked by SQ 22,536. We conclude that DF 2-PGI 2, like PGI 2 and PGE 1, inhibits platelet aggregation by elevating platelet cyclic AMP levels.